The long term objective of our program is to study the role of cell surface lectins and their carbohydrate receptors in cell-cell adhesion. We are focusing on 3 systems: (A) Cellular Slime Molds: We have isolated a receptor for the lectin in P. pallidum. This glycoconjugate, which has the configuration of a large disk, is proposed to act as an extracellular aggregation factor. We will study: the receptor's cell surface distribution by immunocytochemistry and the Heuser technique; its developmental regulation in differentiating amoebae; its mode of attachment to the cell surface; the effect of Fab antibodies against it on cell cohesion; the adhesive properties of variants which lack the receptor; the composition and structural organization of the receptor; (B) Mouse Teratocarcinoma Stem Cells: We will continue our studies of the cell surface mannan/fucan lectin implicated in cell cohesion. Our objectives include: study of the lectin's distribution on stem cells, differentiated derivatives, and mouse embryo cells by immunocytochemistry; determining the effect of Fab antibodies on cell-cell adhesion; the isolation and characterization of variants that lack the lectin; and isolation and characterization of cell surface receptors. (C) Rat Lymphocyte Circulation: A critical event in lymphocyte recirculation is their specific binding to specialized blood vessels (HEVs) in lymphoid organs (nodes, etc.). In an in vitro assay lymphocytes can bind to HEVs in cryostat sections of lymph nodes. Fucoidin, L-fucose, and D-mannose selectively block this interaction, apparently by binding to the lymphocytes. Aims of our studies are: to define precisely the carbohydrate specificity involved; to isolate and characterize lymphoma variants that lack the lectin; to purify and characterize the lectin from cultured lymphoma cells; to determine the effects of Fab against lectin on lymphocyte-HEV binding; to study the distribution of lectin on lymphocyte populations; and to begin the biochemical characterization of the HEV receptor for lymphocyte attachment.